Atrios wraps up a five part discussion of the book by that name here. I added, in the comments (typos corrected):

I read the book. Or at least I tried to. I read through the first chapters as the authors laid out their case, and the more I read the more I found it to be irrelevant. So what if they were right? So what if IQ is an accurate predictor of economic achievement, or that IQ is largely hereditary? (I'm not arguing that any of that is true) What are the policy implications? They may have tried to make the case for dismantling the welfare state but it seems to me that they make the opposite case, that some people are less capable of caring for themselves and will need permanent state subsidized assistance.
Eventually I put the book down and wrote it off as irrelevant to intellectual debate or public policy.

That book certainly doesn't do libertarianism any favors.

You may remember the most controversial aspect of the book is the authors' attempt to tie racial disparities in IQ scores to genetic differences. To be fair this is a small part of the book, and I could never understand why they included it in the book at all. The most cynical explanation would be that the authors were racist and were trying to give racist theories a boost.